1. Field of the Invention
This invention relates generally to an apparatus for measuring the concentration of filamentous microorganisms in a mixture containing the microorganisms, and more particularly ularly to an apparatus for measuring the concentration of the filamentous microorganisms by use of an image processing technique.
2. Description of the Prior Art
In a sewage treatment plant, aeration is made by blowing air into inflowing water inside an aeration tank, organic matters contained in the inflowing water are absorbed by miroorganisms and removed from the water and after the microorganisms are sedimented in a sedimentation basin, a supernatant is discharged. It is therefore necessary to keep those microorganisms which absorb the organic matters well and have high sedimentability. These microorganisms are broadly classified into zoogleal microorganisms and filamentous microorganisms. Among them, if the filamentous microoganisms increase too much (which is called "bulking"), sedimentability drops. If sedimentability drops, the microorganisms will outflow from the sedimentation basin. Accordingly, it is of importance to limit the increase of the filamentous microorganisms. An example of such microorganisms is Sphaerotilus. If the filamentous microorganisms increase too much in the sewage treating process, various problems such as deterioration of the treated water quality and the outflow of the microorganisms will occur.
In a cultivation process of microorganisms, on the other hand, cultivation of filamentous microorganisms is made so as to produce antibiotics such as penicillin, or fermentation is made by utilizing the filamentous microorganisms. These processes are directed to obtain the antibiotics metabolized from the filamentous microorganisms by cultivating them. However, since the amount of the antibiotics cannot be measured within a short period, it is necessary to supervise whether or not the filamentous microorganisms increase.
In both the sewage treating process and the microorganism cultivation process described above, measurement of the amount of the filamentous microorganisms is important for the operation management of these process. At present, the length or the amount of the filamentous microorganisms has been measured by a manual operation of a supervisor (a supervising person). In the sewage treating process, for example, it has been customary to measure the length of the filamentous microorganisms on a photograph by the use of a curvometer or by observation through a microscope. In the microorganism cultivation process, on the other hand, the filamentous microorganisms are sampled and dried, and the dry weight is measured.
Since the conventional measuring method relies on the manual operation by the supervisor, however, several hours of time is necessary for the measurement even by a skilled supervisor. Accordingly, continuous supervision and early detection cannot be made and the management of the cultivation state of the filamentous microorganisms cannot be made, either.
To solve the problems described above, the Applicants of the present invention proposed previously a method of measuring the length of the filamentous microorganisms in Japanese Patent Application No. 140423/1983 (Japanese Patent Laid-Open No. 31889/1985) corresponding to U.S. Pat. No. 4,564,444. This method detects the magnified image of the microorganisms by an industrial television (ITV) camera and recognizes the filamentous microorganisms by the application of an image processing technique.
More definitely, after the image of the filamentous microorganisms is enlarged, the filamentous microorganisms are identified by image processing to extract corresponding pixels, and the recognized pixels are accumulated and then converted to the amount of the filamentous microorganisms. Though the filamentous microorganisms appear filamentary, a certain thickness exists in the filamentary portion. Therefore, the amount of the filamentous microorganisms must be calculated from the number of accumulated pixels in order to accurately measure their amount.
Generally, magnification is adjusted in such a manner that the thickness of the filamentous microorganisms corresponds to one pixel, but the thickness corresponds in practice to one to three pixels due to illumination nonuniformity and noise. In other words, the thickness of the recognized filamentous microorganisms corresponds to one to three pixels. For this reason, even if the pixels are accumulated, the calculated amount becomes greater than the actual amount of the filamentous microorganisms. When the difference between the luminance of the microorganisms and that of the background is small, optical nonuniformity occurs because the background luminance by an optical system cannot be made completely uniform. Accordingly, it is difficult to detect only the microorganisms.